The surface marker CD44 has been identified as one of several markers associated with cancer stem cells (CSCs) in solid tumors but its ubiquitous expression in many cell types including hematopoietic cells has hindered its use in targeting CSCs. In this study, 28 paired primary tumor and adjacent non-tumor gastric tissue samples were analyzed for cell surface protein expression. Cells that expressed pan-CD44 were found to occur at significantly higher frequency in gastric tumor tissues. We identified CD44v8-10 as the predominant CD44 variant expressed in gastric cancer cells and verified its role as a gastric CSC marker by limiting dilution and serial transplantation assays. Parallel experiments using CD133 failed to enrich for gastric CSCs. Analyses of another 26 primary samples showed significant CD44v8-10 upregulation in gastric tumor sites. Exogenous expression of CD44v8-10 but not CD44 standard (CD44s) increased the frequency of tumor initiation in immune-compromised mice. Reciprocal silencing of total CD44 resulted in reduced tumor initiating potential of gastric cancer cells that could be rescued by CD44v8-10 but not CD44s expression. Our findings provide important functional evidence that CD44v8-10 marks human gastric CSCs and contributes to tumor initiation, possibly through enhancing oxidative stress defense. In addition, we showed that CD44v8-10 expression is low in normal tissues. Since CD44 also marks CSCs of numerous human cancers, many of which may also overexpress CD44v8-10, CD44v8-10 may provide an avenue to target CSCs in other human cancers.
Next step of this research
In collaboration with scientists in Singapore Immunology Network, we hope to generate an antibody drug that targets CD44v8-10. As the level of CD44v8-10 varies among patients, we need to continue establishing more patient-derived xenograft models to achieve extensive coverage of the patient spectrum in Singapore. These xenograft models are important as preclinical models for evaluating potential therapeutics that target CD44v8-10.
A) Limiting dilution assays estimating cancer stem cell frequency in unsorted, CD44v+ and CD44v- cell fractions from GC45 and GC84 patient-derived xenografts. Differences between groups were tested for statistical significance using chi-squared test (degrees of freedom=1, 95% confidence intervals). Asterisks denote statistically significant P values. (B) qPCR of CD44s and CD44v8-10 expression in 26 primary tumor samples versus adjacent non-tumor tissue, normalized to 18S rRNA internal control. Horizontal bars represent the mean value. Paired Student’s t-test was performed for statistical significance.
Authors: Wen Min Lau1,4, Eileen Teng1,4, Hui Shan Chong1, Kirsten Anne Pagaduan Lopez1, Amy Yuh Ling Tay2, Manuel Salto-Tellez3,1, Asim Shabbir2, Jimmy Bok Yan So2,5 and Shing Leng Chan1,5,6
- Cancer Science Institute of Singapore, National University of Singapore. 14 Medical Drive, MD6, #12-01, Singapore 117599
- Department of Surgery, National University of Singapore, Singapore. NUHS Tower Block Level 8,1E Kent Ridge Road, Singapore 119228.
- Centre for Cancer Research & Cell Biology, Queen’s University Belfast, 97 Lisburn Road, Belfast BT9 7BL, Northern Ireland, UK.
- These authors contributed equally to this work.
- The project is conceptualized by these authors.
- Corresponding author.